With regard to monitoring systems to monitor a vehicle's surroundings, a security system is known in which upon detection of external stimulus such as detected by a door contact sensor, a camera is employed to capture the surroundings and the image information will be transmitted to an outside mobile phone or the like. See, for example, JP-A No. 2006-107279. However, when a captured image of the camera is sent as it is, i.e., without change, there is a large burden of communication time and cost.